This invention relates to circuit breaker mechanisms and, more particularly, to arc chute assemblies for circuit breaker mechanisms.
Arc chutes or arc shields are commonly used to confine and extinguish an electric arc that is produced when the circuit breaker mechanism is tripped and the contacts are rapidly opened. A molded case circuit breaker mechanism 10 is shown in FIG. 1 comprising a case 12 with the cover removed to show the interior components depicted in an open position. The current carrying components include two fixed contacts 14, 16 and two movable contacts 18, 20 attached to an operating mechanism 22 by means of a movable contact arm 24. The operating mechanism is refrained from driving the movable contact arm and movable contact to the open position under the bias provided by a pair of powerful operating springs (not shown). The two pairs of springs provide a floating assembly of the operating mechanism 22 in an orifice 28 allowing rotation of the contact arm 24 around an axis 30. Pairs of springs also provide the contact pressure in the closed position of the pole. Pairs of springs are arranged symmetrically with respect to axis of rotation 30 of contact arm 24, so as to exert in any position of the contact arm 24, a return torque of the contact arm 24 to the closed position.
In the closed position of the contact arm 24, the fixed contact 14 cooperates with the movable contact 18 borne by the contact arm 24, whereas the fixed contact 16 cooperates with the movable contact 20. The current input at a given moment via an input conductor 32 flows through the fixed contacts 14, 16, contact arm 24, and movable contacts 18, 20, and is output on the opposite side via a conductor 34. It can be seen that the ends 36, 38 of conductors 32, 34 have flowing in them currents of opposite polarities to the currents flowing in the contact arm 24, thereby generating a repulsion force moving the contact arm 24 to the open position. This looped trajectory in the zone of the contacts 14, 16, 18, 20 generates a magnetic blowout field.
The magnetic blowout field comprises an arc plasma discharge that momentarily stays for a short while in the zone of fixed contacts 14, 16 and then moves toward arc chute assemblies 40, 42 in accordance with a sudden upward bouncing of the movable contacts 18, 20 as a sudden disconnection.
Then, as the movable contacts 18, 20 move upwards in the direction of arrow 43, the stable contacts 14, 16 become further distanced from the movable contacts 18, 20, and accordingly the arc moves toward an internal portion of arc chute assemblies 40, 42 by an electromagnetic force generated between the a plurality of arc chute plates 44 and the arc current (FIG. 2).
Referring now to FIG. 2, the plasma arc discharge that has moved inside the arc chute plates 44 are serially partitioned according to the arc chute plates aligned on every other floor therein, and the arc resistance becomes rapidly increased and accordingly the arc voltage becomes rapidly increased by related factors, such as cathode effect of the plates 44 in which when the arc comes into the arc chute assemblies 40, 42, the plates 44 are respectively turned to positive poles or negative poles, a cooling effect in which the arc is partitioned into shorter arcs between the plates 44 and extinguished in the air by cooling, and a pressure effect according to an arc energy by an increased magnetic flux density with regard to a pressure increase in the arc chute assemblies 40, 42.
Referring now to FIG. 3, the conventional arc chute assembly for extinguishing plasma arc discharge will now be described. The conventional arc chute assembly 40 includes plurality of arc chute piates 44 formed of a metal or an alloy of metals for inducing magnetism, and a plurality of sidewalls 46 formed of insulation material.
Arc chute plates 44 respectively include a plurality of engagement protrusions 48 extended from each side thereof and cut off by the respective centers thereof. The sidewalls 46 include a plurality of slots 50 for receiving corresponding ones of the engagement protrusions 48.
The combining steps between the plates 44 and the sidewalls 46 for forming the arc chute assemblies 40, 42 will now be described. The plates 44 including the engagement protrusions 48 are fixed using a gig and then the plates 44 are respectively inserted into a corresponding one of the engagement slots 50 formed in the sidewalks 46. In order for the plates 44 not to escape from the sidewalls 46, the sidewalls 46 are bound by a rubber string.
The respective cut-off portions of the engagement protrusions 48 are opened to each side thereof by employing a riveting process, thereby fixing the plates 44 to the sidewalls 46.
Likewise, plurality of plates 44 are stacked with a space therebetween between the sidewalls 46, and the assembled arc chute assembly 40 is mounted in the arc extinguishing chamber provided in the circuit breaker. However, the conventional arc chute assembly 40 allows the plates 44 to be inserted into the sidewalls 46, and in order for the plates 44 not to be released from the sidewalls 46, the sidewalls 46 are fixed by use of a rubber string and there is further followed a riveting process for the fixture.
Referring again to FIG. 2, the present arc chute design depicts how hot arc plasma gas generated by the opening operation between the stationary and movable contacts flows through a set of iron arc plates in the direction of arrows 52.
As a result, there is a need for an arc chute designed to prevent discharged arc plasma gas from collecting on the contact arm.
There is also a need for an arc chute designed to promote the flow of discharged arc plasma gas through the spaces between a set of arc plates.
There is also a need for an arc chute plate design that minimizes the drag/reflecting areas at the edges of the arc chute plates.
There is also a need for an arc chute plate design having aerodynamically cut edges to facilitate the easy flow of arc plasma gas into the chute, and out of it.
There is also a need for an arc chute plate design having aerodynamically cut edges to facilitate minimal reflection of the arc plasma wave.
The exemplary embodiments include an arc chute assembly for a circuit breaker mechanism having a pair of support members and a plurality of plates being supported by the pair of support members. The assembly has a plurality of plates that define a plurality of openings where the support members are positioned so as to define the plurality of openings. The plates each have a pair of tabs which are received in a corresponding pair of openings within each of the support members. The plates are configured to have at least one aerodynamic feature to facilitate the movement and extinguishing of discharged arc plasma waves and the plates are configured to have an opening along the periphery of one of the sides of said plates. The openings are configured to facilitate the movement and extinguishing of discharged arc plasma waves.
These and other features and advantages of the present invention will be apparent from the following brief description of the drawings, detailed description, and appended claims and drawings.